I. Field of the Invention
The present invention relates to methods and apparatus for improving the operation of a gamma camera.
II. Background Information
Gamma cameras are employed to measure gamma rays radiated from a gamma ray source. Gamma cameras typically comprise a gamma ray collimator, a thallium-doped sodium iodide scintillation crystal, a light guide, and a plurality of photomultiplier tubes. The collimator is arranged to permit a selected orientation of gamma rays from the gamma ray source to strike one surface of the sodium iodide scintillation crystal. The photomultiplier tubes are arranged adjacent the opposite surface of the scintillation crystal and are arranged to receive light emanating from the scintillation crystal in response to the incident gamma rays. The light guide is arranged between the scintillation crystal and the photomultiplier tubes to effect the transfer of light from the liquid scintillation crystal to the photomultiplier tubes.
Standard thallium-doped sodium iodide scintillation crystals have a particular response time during normal operation at room temperature.
It is an object of the subject invention to improve the response time of a gamma ray camera, utilizing the fact that pure, undoped sodium iodide has substantially shorter response time than thallium-doped sodium iodide. Pure, undoped sodium iodide is normally not used because its light output is so low that gamma-camera performance would be unacceptably poor. However, light output increases as temperature is lowered. It is an object of this invention to provide a practical means of operating a crystal at reduced temperature.
Additional objects and advantages of the invention will be set forth in the description which follows and in part will be obvious from the description or may be learned by practice of the invention.